138 



The Use of Manures in Forestry. [may, 



in the better types of soils the necessary food salts are present 

 in sufficient quantity, and that artificial manuring is only 

 of importance where the soil has deteriorated, or in cases 

 where it is desired to carry a crop quickly over some critical 

 period, such as danger from frost or game. Owing to the 

 relatively deep position of the roots, manuring with ordinary 

 manures is practically without result on middle-aged woods. 

 The only possibility of encouraging the development of such 

 woods seems to lie in bringing about the quicker decomposi- 

 tion of the fallen leaves and twigs, either by working the 

 soil, or, better still, by the application of lime. The irriga- 

 tion of a sixty-year-old pine wood at the Berlin Irrigation 

 Works with sewage water was tried, but was a distinct failure, 

 as a monthly application during the chief vegetation period 

 of the year caused, in two years, the death of many stems. 

 Considerably better results were obtained by irrigation experi- 

 ments at Gorlitz, where irrigated plantations of spruce, 

 Weymouth pine, and Scotch pine showed a better growth 

 than those not irrigated. In this case, however, the woods 

 treated were, at the most, thirty years old, and the importance 

 of age seems to be shown by the fact that at the Berlin Irriga- 

 tion Works new plantations on irrigated areas have shown 

 good growth. A form of manuring in pine woods which 

 offers prospects of success is the covering of the soil with a 

 layer up to 8 inches deep of city refuse. The City of Berlin 

 has experimented in this direction, with the result that after 

 two years the pine woods treated showed excellent develop- 

 ment. 



It is, however, in the planting and early growth of trees 

 on poor soils that artificial manuring assumes importance. 

 Soil analyses show that in poor, sandy soils the nitrogen 

 contents have been reduced to a minimum, and consequently 

 this element is the chief consideration ; phosphoric acid also 

 plays an important part, but potash is only of subordinate 

 importance. As nitrate of soda and sulphate of ammonia 

 are too rapid in their action for a slow-growing crop, the 

 chief difficulty in manuring on sandy soils is to supply 

 nitrogen in a slowly available form at the least cost. Up 

 to the present, experiments indicate that this can best be 

 done by utilising the nitrogen contained in plant residues in 



